The United States online retail giant's revolutionary project still needs extra safety testing and federal approval, but Mr Bezos believes that Amazon 'Prime Air' would be up and running within four to five years.

"These are effectively drones but there's no reason that they can't be used as delivery vehicles," Bezos told CBS television's 60 Minutes program.

"I know this looks like science fiction. It's not.

"We can do half-hour delivery... and we can carry objects, we think, up to five pounds (2.3 kilograms), which covers 86 per cent of the items that we deliver."

But Microsoft co-founder Gates told CNN the plan might not be realistic, although he acknowledged the notion of drones could be useful for things such as charitable aid.

"I would say he's probably on the optimistic or perhaps overoptimistic end of that," Mr Gates said.

"It's great that people have dreams like that.

"If we can make the cost of delivery easier, then it's not just books, it's getting supplies out to people in tough places.

"Drones overall will be more impactful than I think people recognise in positive ways to help society."

A video posted on Amazon's website shows a prototype drone.

The body of the device is about the size of a flat-screen monitor, and it is attached to eight small helicopter rotors and sits on four tall legs.

The claws under the belly of the "octocopter" then latch onto a standard-sized plastic bucket that rolls down a conveyer belt at Amazon's distribution centre. Inside the bucket is the order.

The drone lifts off and whizzes into the air like a giant mechanical insect to deliver the package just 30 minutes after clicking the "pay" button on Amazon.com.

Then it buzzes back into the air and returns to base.

The mini-drones are powered by environmentally friendly electric motors and can cover areas within a 16 kilometre radius of fulfilment centres, thus covering a significant portion of the population in urban areas.

Project could be ready by 2015

The drones would operate autonomously and follow the GPS coordinates they receive to drop the items off at target locations.

He also claims they are safe because the prototype has redundant motors that will keep it in the air and prevent it from crashing.

"The hard part here is putting in all the redundancy, all the reliability, all the systems you need to say, 'Look, this thing can't land on somebody's head while they're walking around their neighbourhood,'" he told CBS.

Amazon said the octocopters would be "ready to enter commercial operations as soon as the necessary regulations are in place," noting that the Federal Aviation Administration was hard at work hammering out rules for the use of unmanned aerial vehicles.

Amazon projected a more optimistic timeline than Mr Bezos for the project to be activated, saying the FAA's rules could be in place as early as 2015, and that Amazon Prime Air would be ready at that time.

Mr Bezos hinted that part of the motivation behind the mini-drones was to make sure Amazon remains at the cutting edge of the retail industry.

"Companies have short life spans... and Amazon will be disrupted one day," he said.

"I would love for it to be after I'm dead."

If the plan succeeds other retailers such as Walmart, or even the local pizza store, could also start home deliveries via drone.

Comments on Twitter about the program ranged from amazed to humorous.

"If this weren't on the CBS website, I would think this Amazon drone thing was an Onion article," wrote Iris Blasi, referring to the popular satirical tabloid.

FAA chief Michael Huerta earlier said he expects some 7,500 small unmanned aircraft buzzing in the US skies in the next five years.

Michael Toscano, head of the Association for Unmanned Vehicle Systems International (AUVSI), predicted that a booming market for civilian drones will lead to the creation of 100,000 jobs over the next decade.